Processing method for nano-size substance

ABSTRACT

According to this invention, an active portion in nano-size substance is destroyed selectively by applying an electric potential to the nano-size substance having a network structure of carbon at an outer shell thereof in electrolytic solution. For example, an electric potential of 1.20 to 1.60 V (RHE) is applied to carbon nanotube in electrolytic solution so as to oxidize the active portion in the carbon nanotubes selectively and remove the ends of them. Consequently, an open end is created in the carbon nanotube.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a processing method for nano-size substance having carbon network structure at its outer shell and more particularly, a processing method preferable for opening the ends of the carbon nanotubes.

[0002] In recent years, carbon nanotube which is carbon material having a stereo structure, as nano-size substance having the carbon network structure at its outer shell has been developed actively and the carbon nanotube is formed according to a well known method such as arc discharge method, laser evaporation method and chemical vapor deposition (CVD) technique.

[0003] Further, the metallic behavior, electric characteristic such as semiconductor-like behavior and mechanical characteristic indicating an excellent strength despite light weight have attracted attentions as well as its peculiar structure, so that a large number of researches are carried out successfully. Using those characteristics, a wide application is expected in hydrogen, methane absorbing material, selectively absorbing material for use for gas separation based on pressure swing adsorption method (PSA) or the like, material of fuel cell electrode, material of electrochemical supercapacitor electrode, material of highly functional lithium cell anode, nanodevices and light weight, high-strength composite material. In fact, actual use thereof has been already started in, for example, adding to resin used in tray for carrying electronic parts or automobile mounting parts. The possibility that the aforementioned applications may be achieved is very high.

[0004] This carbon nanotube includes single-walled carbon nanotube having a single carbon layer structure and multi-walled carbon nanotube having two or more carbon layer structure.

[0005] The above mentioned single-walled carbon nanotube is formed in a condition that its terminal is closed with fullerene semi-sphere and if it is intended to incorporate some substance in a hollow space inside that single-walled carbon nanotube, these ends need to be removed.

[0006] As the above-mentioned method for removing the terminal, conventionally, there are a method of using oxidative acid solution such as nitric acid, mixed acid so as to make it react with the carbon nanotube (various chemical reactions, mainly oxidizing reaction, selectively occurs at the terminal of the carbon nanotube, so the ends are removed. The principle of this method is considered to be based on the fact that the chemical reactivities of the five-membered ring and six-membered ring composing the carbon nanotube are different in terms of molecular level. The five-membered ring has a higher chemical reactivity than the six-membered ring.), a method of irradiating with ultrasonic wave so as to raise reactivity (applying ultrasonic vibration destroys the terminal of the carbon nanotube selectively) and a method of oxidizing at about 400° C. in dry air.

[0007] These methods not only remove the terminals but also oxidize (burn) the nanotube in a wide range thereby producing possibility that the yield drops or the peculiar nanotube structure may be destroyed. That is, although oxidizing reaction needs to be controlled accurately to remove the ends of carbon nanotubes, the conventional methods are incapable of executing such accurate control.

[0008] In the meantime, the process of opening a carbon nanotube individually is not profitable industrially. Therefore, in the present invention, the carbon nanotube is treated as an aggregate and it is intended to remove the ends from each carbon nanotube composing that aggregate. The removal of the ends of carbon nanotubes refer to oxidizing of the terminal selectively because the terminal of the carbon nanotube has a larger structural distortion than its side portion so that it reacts highly to oxidation.

[0009] Further, the present invention intends to destroy a specific portion in nano-size substance having carbon network structure at its outer shell to change the characteristic of the nano-size substance, thereby aiming at development for new application.

[0010] If oxidizing condition is strong (the oxidizing condition depends on concentration of oxidizing agent, reaction time, heating temperature and the like), the nanotube itself is destroyed, so that best use of the peculiar pore inside the nanotube may not be achieved.

[0011] In case of heat treatment for example, uniform oxidizing condition is difficult to achieve on not only entire nanotube aggregate but also nano-scale level, because activity of oxygen molecules contributes essentially in microscopic point of view as well as temperature gradient in a sample arises (there is a possibility that a sufficiently oxidized portion and not so sufficiently oxidized portion may be produced because temperature distribution arises in the sample).

SUMMARY OF THE INVENTION

[0012] Accordingly, in order to open the carbon nanotube by carrying out oxidation treatment more selectively, the present invention applies electrochemical treatment.

[0013] If electrochemical oxidation treatment is carried out with a predetermined potential, the ends of the carbon nanotube is oxidized and removed selectively so as to obtain open-ended carbon nanotube. The reason for this is that an ideally linear single-walled nanotube closed with fullerene semi-sphere has totally 12 five-membered rings at both ends of the tube as shown in the structure of FIG. 1. A carbon of the five-membered ring has a larger distortion from sp² hybrid orbital (having a bond angle of 120° in the same plane) than the six-membered ring and is less stable in terms of energy, so that it is more highly active to chemical reaction and therefore more likely to be oxidized.

[0014] If an electric potential is applied intermittently, the efficiency of destruction of an active portion is improved. In other words, if the electric potential is applied continuously, as its reaction is progressed, water absorbing to the surface of nano-size substance is consumed and the reaction is dulled, so that current flow is stopped. On the other hand, if processing electric potential is interrupted, water molecules dissipate to the surface of the nano-size substance so that water is supplied. Then, if the electric potential is applied again, current flow is started. Repeating this procedure enables the processing time to be shortened.

[0015] Interrupting the supply of the electric potential reduces a difference in water distribution between a region likely to be supplied by dissipation of water molecules and a region unlikely to be supplied, so that uniform processing on the entire nanotube aggregate, which is an initial purpose of the present invention, is achieved.

[0016] If the dissipation of water molecules is secured, the intermittent application of the electric potential is not restricted to any particular type, but for example, pulse-like potential can be applied. Alternatively, sine wave like potential can be applied such that its maximum amplitude is equal to the aforementioned oxidizing potential.

[0017] As for the intermittent application condition, when no potential is applied, it does not have to be 0 V (RHE) but can be less than the aforementioned oxidizing potential (1.0 V (RHE)). Further, this can be deflected to the side of reduction potential (minus potential).

[0018] It is considered that actual carbon nanotube includes seven-membered ring and the seven-membered ring is likely to be oxidized for the same reason as the five-membered ring (as compared to the six-membered ring). Thus, if the applied potential is controlled precisely, only the five-membered ring or the seven-membered ring can be oxidized selectively. Further, this applied potential can be controlled highly accurately by using a potentiostat.

[0019] Because the aggregate (electrode) of the carbon nanotube has a small resistance (less than 1 Ω), potential distribution of the entire carbon nanotube aggregate is small. Because uniform potential is applied to the entire aggregate, oxidizing reaction occurs uniformly, so that opening of the carbon nanotubes are carried out uniformly in the aggregate. As a result, uniform oxidation treatment having a reaction condition restricted to a small range, which is difficult in the conventional acid treatment or heat treatment, can be achieved.

[0020] Consequently, accurate reaction control necessary for removing the ends of the carbon nanotubes as its aggregate is made possible.

[0021] If an electric potential for reducing the carbon nanotube is supplied, it is possible to reduce the end portion selectively and destroy or remove it for the same reason as the case of oxidation mentioned above.

[0022] As for the configuration of an apparatus for removing the ends, for example, a carbon nanotube aggregate itself is formed in the form of an electrode and platinum is employed as a counter electrode. As oxidizing potential to the nanotube electrode, a specific potential in a range of 1.00 to 1.60 V (RHE: potential with respect to equilibrium hydrogen electrode, description of the “RHE is omitted in some places of this specification) is applied with pulse so as to oxidize part of the carbon nanotubes, removing the ends of them. More preferably, the oxidizing potential is 1.20 V to 1.60 V (RHE).

[0023] Conversely, in case of reducing part of the carbon nanotube, its reduction potential is in a range of −0.5 to −1.5 V.

[0024] For an electric potential range for use, it is necessary to use a gold mesh, glassy carbon or the like electrochemically stable as a wiring which makes contact with electrolytic solution. The carbon nanotube after oxidation treatment can be taken out of a cell and separated easily with water, organic solution (toluene or the like) and collected. The temperature of the electrolytic solution is 20° C.

[0025] According to a first aspect of the present invention, by applying an electric potential to nano-size substance having a carbon network structure at an outer shell thereof in electrolytic solution, an active portion in the nano-size substance is destroyed selectively. Consequently, the terminal can be removed from, for example, the carbon nanotube which is a nano-size substance.

[0026] Such an electrochemical processing is capable of controlling a voltage to be applied to each electrode with an electric potential supplying means such as a potentiostat highly accurately. Further, because resistance of the nano-size substance itself is small (less than 1 Ω), uniform potential is applied to a nano-size substance aggregate so that reaction condition for the entire nano-size substance aggregate is made uniform. Thus, a processing with distribution of the reaction condition restricted to a small range, which is difficult for the conventional acid treatment or heat treatment, is achieved, so that an accurate reaction control necessary for destroying the active portion of the nano-size substance selectively is enabled.

[0027] According to a second aspect of the present invention, the nano-size substance having a carbon network structure at an outer shell is one type or two or more types selected from carbon nanotube, fullerene, carbon nano-horn and modified types.

[0028] The carbon nanotube mentioned in the present invention includes a single-walled carbon nanotube which is a microscopic hollow tube produced when graphite of a single atomic layer, namely graphene is rounded cylindrically without any joint, its diameter being on nanometer order, and multi-walled carbon nanotube produced when two to several tens graphenes are overlaid, its diameter being in a range of 2 nm to 50 nm.

[0029] According to a third aspect of the present invention, the nano-size substance which is a processing object has a space substantially closed by the outer shell having the network structure of the carbon like carbon nanotube mentioned above. By destroying partially the outer shell of that substance, the closed space is opened, so that the space (nano-size space) can be available.

[0030] According to a fourth aspect of the present invention, the active portion in the carbon network structure of the nano-size substance is five-membered ring or seven-membered ring. For example, a tube-like portion of carbon nanotube is formed of the six-membered ring of carbon and the five-membered ring structure or the seven-membered ring structure exists at the end portion or a bent portion. Because the five-membered ring and the seven-membered ring have a higher chemical reactivity (activity) than the six-membered ring, that portion is destroyed selectively by supplying the carbon nanotube with a difference of potential, so as to open the carbon nanotubes.

[0031] According to a fifth aspect of the present invention, the aforementioned oxidizing potential is 1.00 to 1.60 V (RHE). If this potential is applied, the active portion of the nano-size substance is destroyed selectively. If the applied potential is less than 1.00 V (RHE), the reaction is dull and if the applied potential (RHE) exceeds 1.60 V, oxidation of the six-membered ring can be progressed. A more preferable applied potential is 1.20 to 1.60 V (RHE). A still more preferable applied potential is 1.35 to 1.50 V (RHE).

[0032] The active portion of the carbon network structure of the nano-size substance can be destroyed selectively by reduction. In this case, a preferable reduction potential is −0.5 to −1.5 V (RHE).

[0033] Adjusting chemical/physical environments in parallel to or before/after the aforementioned electrochemical processing enables to enhance destruction of the active portion.

[0034] For example, as a chemical treatment, pre-processing can be carried out with thin acid solution. It is also permissible to add oxidant such as hydrogen peroxide solution, nitric acid, mixed acid, potassium permanganate or reductant such as alcohol, aldehyde, hydrazine to electrolytic solution for use. Using such oxidant or reductant enables to enhance oxidizing reaction or reducing reaction. It is permissible to heat to raise a reaction temperature.

[0035] On the other hand, as physical processing, it is permissible to apply ultrasonic wave and/or magnetic field as well as potential.

[0036] Those skilled in art can estimate easily that if oxidant or reductant is added, the applied potential may be changed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] These and other objects and technical advantages of the present invention will be readily apparent from the following description of the preferred exemplary embodiments of the invention in conjunction with the accompanying drawings, in which:

[0038]FIG. 1 is a schematic diagram showing the structure of the carbon nanotube;

[0039]FIG. 2 is a schematic diagram showing the structure of an electrochemical processing apparatus of an embodiment;

[0040]FIG. 3 is a diagram showing an example of potential pulse sequence to be applied to the carbon nanotube;

[0041]FIG. 4 is a diagram showing other example of potential pulse sequence to be applied to the carbon nanotube;

[0042] FIGS. 5(A), (B) show cyclic voltammetry (CV) after oxidation treatment is carried out at 1.35 V and 1.50 V respectively while state before oxidation treatment is indicated with solid line and state after oxidation treatment is indicated with dotted line;

[0043]FIG. 6 is a diagram showing pore distribution estimation principle with XeNMR;

[0044]FIG. 7 shows a Xe NMR spectrum of sample treated at 1.35 V;

[0045]FIG. 8 shows a Xe NMR spectrum of a un-treated sample;

[0046]FIG. 9 is a graph showing pressure dependence of Xe chemical shift value relative to voltage; and

[0047]FIG. 10 is a graph showing a result of plotting pores diameter with an inverse number of δ.

DESCRIPTION OF THE PREFERED EMBODIMENTS

[0048] The preferred embodiment of the present invention will be described about the carbon nanotube as the nano substance having carbon network structure at its outer shell.

[0049]FIG. 2 shows an example of an electrochemical oxidation treatment unit 1 of the embodiment of the present invention. This oxidation treatment unit 1 comprises a working electrode chamber 10, a counter electrode chamber 20, a equilibrium hydrogen electrode (RHE) chamber 30 and a control portion 40. The working electrode chamber 10 and the counter electrode chamber 20 communicates with each other through a pipe and the working electrode chamber 10 also communicates with the equilibrium hydrogen electrode (RHE) chamber 30 through a pipe. Each chamber is filled with sulfuric solution (1.0 M) as electrolytic solution 7. As the electrolytic solution 7, it is also permissible to use ordinary acid solution, alkali solution or normal salt solution. This experiment was also carried out with the temperature of the electrolytic solution 7 set at room temperature (20° C.).

[0050] The working electrode 11 is dipped in the working electrode chamber 10. A single-walled carbon nanotube HiPCO perchased from Carbon Nanotechnologies Incorporated having 90% purity dispersed in toluene was applied to 4 cm² gold mesh (100-mesh screen) and by drying this net, a nanotube electrode was produced. As electrolytic solution for removing the ends of carbon nanotubes electrochemically in case where carbon nanotube of 18-20 mg is contained in an electrode, 1.0M H₂SO₄ solution was used. An applied potential is pulse like and oxidation treatment was carried out repeatedly.

[0051]FIG. 3 shows a pulse sequence of the embodiment. The oxidation treatment was carried out under two conditions using 1.35 V and 1.50 V as an applied potential (treatment potential). When a treatment pulse falls, the electric potential is dropped to about 200 mV. Under a lower potential, oxygen is generated remarkably at the counter electrode, which is not preferable.

[0052] The upper limit of applied potential is 1.50 V or 1.35 V while the lower limit thereof is 0.2 V (200 mV). The upper limit voltage was applied for 60 seconds and then the lower limit voltage was applied for 30 seconds and this cycle was repeated for one hour. The reason why the pulse sequence is employed is to prevent current flow from being stopped because electrolytic solution is consumed as reaction progresses if electric potential is supplied continuously.

[0053] The reason why argon gas is supplied is to prevent oxygen dissolved in the electrolytic solution from affecting. As a result, the accuracy and quality of obtained data are improved.

[0054]FIG. 4 shows the pulse sequence of other example. The example of FIG. 4 aims at removing the ends by supplying a carbon nanotube with reduction potential. Preferably, its processing potential is −0.50 to −1.50 V (RHE).

[0055] As a result of NMR analysis for the applied potential, it was found that a upper limit potential of an applied potential is preferred to be 1.2 to 1.6 V (RHE) if the electrolytic solution is at the room temperature (20° C.). More preferably, it is 1.35 to 1.50 V (RHE).

[0056] In the meantime, those skilled in art can estimate easily that applied potential may go up/down depending on the temperature of electrolytic solution.

[0057]FIG. 5 shows a result of cyclic voltammetry executed using an electrode after oxidation treatment.

[0058] FIGS. 5(A), (B) show cyclic voltammogram (CV) after oxidation treatment is executed at 1.35 V and 1.50 V respectively, while the state before the oxidation treatment is indicated with solid line and the state after the oxidation treatment is indicated with dotted line.

[0059] In case where a sample is treated at 1.35 V, before the oxidation treatment is carried out, the amount of current increases rapidly from around 1.00 V on the abscissa axis of the graph (indicates that this portion is oxidized by CV) and this increase of the current is recognized up to near 1.60 V. The reason why scanning potential is raised up to around 1.60 V is to compare current states at the upper limit of pulse potential or near 1.35 V in FIG. 5(A).

[0060] If looking at the dotted lines, although current rises from around 1.20 V after the oxidation treatment, it does not increase so much as before the oxidation treatment.

[0061] The arrows indicate the upper potential of 1.35 V applied with pulse. If the portions at the upper limit potential are compared, whether or not the oxidation is actually achieved can be determined. Even if the comparison is done at this point, it will be found that the carbon nanotube is oxidized more so that current does not flow easily under this cyclic voltammetry.

[0062] If looking at the dotted line in case of a sample treated at 1.50 V, although current rises from around 1.20 V after the oxidation treatment, the current amount does not increase so much as before the oxidation treatment and if comparing with the case of 1.35 V, current does not flow as easily. The arrow indicates the upper limit potential of 1.50 V applied with pulse. If the portion at the upper limit potential is compared, whether or not the oxidation is actually achieved can be determined. Even if the comparison is done at this point, it is found that the carbon nanotube is oxidized more so that current does not flow easily under this cyclic voltammetry. Further, because current more unlikely flows at 1.50 V, which is a higher potential than 1.35 V, it can be estimated that oxidizing force is larger as the electric potential increases.

[0063] Although there is some point where the current value increases in a sample subjected to the oxidation treatment at the electric potential of below 1.0 V, the carbon nanotube is not oxidized because oxidation of carbon never occurs below 1.0 V (this has been confirmed with activated carbon) and it is considered that current originated from formation of electric double-layers was observed.

[0064]FIG. 5 testifies that the carbon nanotube is oxidized electrochemically. Further, because the current value is not zero, it is estimated that the five-membered ring or the seven-membered ring in the carbon nanotube is selectively oxidized while the six-membered ring remains.

[0065]FIG. 5(A) shows a sample processed at 1.35 V and the integrated amount of oxidizing charge applied at this time is 39 C (20.3 mg in terms of nanotube amount). FIG. 5(B) shows a case where the processing is carried out at 1.50 V and the integrated amount of applied charge at this time is 176 C (21.0 mg). Oxidizing current in an applied potential range (indicated with an arrow) decreases if the states before and after processing are compared, which indicates that irreversible oxidizing action was progressed.

[0066]¹²⁹Xe NMR measurement was carried out on samples processed at 1.35 V and 1.50 V under pulse condition of FIG. 3 and a not-processed sample in order to recognize the effect of opening the carbon nanotubes. According to this measurement method, information about pore (d<5 nm) existing in the sample can be obtained from Xe chemical shift value.

[0067] Pressure dependence of the ¹²⁹Xe NMR chemical shift (δ) is measured. The δ is shifted to a lower magnetic field as Xe gas pressure increases and the pore is evaluated based on a value extrapolated at 0 atmospheric pressure.

[0068] That is, the pore is smaller as the chemical shift value is located at a lower magnetic field side while larger as close to 0 ppm. There is data about the pore and chemical shift value of activated carbon having a narrow pore distribution, zeolite and polymer. If Xe chemical shift values before/after electrochemical oxidation treatment on the carbon nanotube are compared with reported data and examined, removal of the ends of carbon nanotubes can be recognizede. FIG. 6 shows its schematic view.

[0069]¹²⁹Xe NMR spectra were recorded with single pulse sequence with 3 μs of pulse width using a Bruker MSL-200 type spectrometer at the Lamor frequency of 55.57 MHz. The measurement was carried out in a pressure range of 0.05 to 5.30 Mpa. The sample temperature at the time of measurement was kept at 298 K.

[0070] A sample of about 40 mg was put into a NMR tube 5 mm in diameter, 25 mm long and fixed with quartz wool. After vacuum degassing for an hour at 200° C., the sample was set at a high-pressure Xe NMR dedicated probe (Chem. Phys. Lett., 340 (2001) 473.). Then, after vacuum degassing on the sample for an hour at 298K, Xe gas was adjusted to a desired pressure and ¹²⁹Xe NMR measurement was carried out. Upon this measurement, Xe gas was introduced to the probe through a pipe as required and the pressure dependency of NMR spectrum was investigated.

[0071]FIG. 7 shows a result of measurement on the sample treated at 1.35 V and FIG. 8 shows the case of a sample before treatment. In the sample treated at 1.35 V, a peak (indicated with *) considered to be originated from Xe adsorbing to micro pore was observed on the side of low magnetic field and changed toward a lower magnetic field as pressure increased. This pressure dependency, which is observed when a single micro or meso pore exists in a sample, is a characteristic pressure dependency found in Xe NMR. At this measurement, repeating time was set to 1 s and the peak strength of adsorbed Xe was substantially the same compared with the case of 5 s. Spin-lattice relaxation time (T1) is considered to be shorter than 1 s. A sharp peak around 0 ppm is originated from free Xe in gaseous condition.

[0072] On the other hand, because the pressure dependency as shown in FIG. 7 is not found in a sample before processing and the peak of the adsorbed Xe is much broader than the case of a processed sample, it is considered that no uniform pore exists. The observed peak is considered to be originated from Xe adsorbing to a gap between nanotube bundles or between nanotubes. The reason why the specific surface area of a sample before processing is as large as 700 m²/g is that there exist a large number of the aforementioned gaps.

[0073] As regards the peak of the adsorbed Xe shown in FIG. 7, changes in chemical shift value relative to pressure is indicated with a black mark in FIG. 9. Although the chemical shift value changes to lower magnetic field in a region in which pressure is 0.1 to 1.0 MPs, the change in a higher-pressure region is small. Recently, a research by Ueda et al. has investigated pressure dependence of Xe NMR chemical shift value in a system in which Xe adsorbs in pore of activated carbon fiber (ACF) in detail and this pressure dependence could be analyzed assuming the Langmuir type adsorption. That is, the chemical shift value δ(P) has a relation expressed by a following equation with the shift arising from the collisions between Xe and walled-surface δXe-wall, the value relating to the density of the Xe in the pore δXe-Xe^(max), K is the equilibrium constant between the Xe adsorbed into the pore and the Xe gas.

Equation 1

[0074] As for the result of the sample processed at 1.35 V (triangles), the result of simulation with δXe-wall=87 ppm, δXe-Xe^(max)=80 ppm, K=2.5 Mpa⁻¹ is shown by a straight line in FIG. 9. The result of a sample processed at 1.50 V is indicated by dotted line. At this time, the condition is δXe-wall=110 ppm, δXe-Xe^(max)=90 ppm, K=2.7 Mpa⁻¹. The value δXe-wall extrapolated to 0 atmospheric pressure corresponds to the size of a pore Xe adsorbed. According to the research done by Ueda et al., it was found that δXe-wall was 95 ppm if the pore was 1 nm, 80 ppm if 1.5 nm and 71 ppm if 2.0 nm. It was empirically confirmed that the XeNMR chemical shift value is inversely proportional to the diameter (d) of the pore (Chem. Phys. Lett., 136, (1987) 314.).

[0075] In FIG. 10, the result of ACF is plotted with an inverse number of δ with respect to the diameter of the pore. If a very excellent linearity is indicated in the region of the diameter of the pore so that a regression curve is produced, it is expressed with a solid line in FIG. 10. If the diameter of the pore was obtained from the value of δXe-wall of this embodiment, it was 1.2 nm (1.35 V) and 0.6 nm (1.50 V). Because the purity of carbon nanotube contained in the sample is about 90% and that diameter is distributed over 0.9 to 1.4 nm, it is concluded that the Xe absorption site is inside the nanotube.

[0076] Because as a result of the example 2, a peak of xenon contained in the carbon nanotube was found, the opening of carbon nanotubes was confirmed.

[0077] By introducing a new electrochemical method capable of achieving accurate, uniform processing, the removal of the ends of the carbon nanotubes with maintaining the cylindrical structure is achieved. Consequently, the yield of the open-ended carbon nanotube is improved there by making it possible to reduce production cost thereof.

[0078] Use of internal space inside the carbon nanotube enables to provide novel functional materials such as gas absorbing material which absorbs physically a large amount of hydrogen, methane or the like, gas separating material for use in pressure swing adsorption (PSA) technique, material of a novel anode of lithium ion cell, electrode material which realizes an electrochemical supercapacitor having a large capacity by introducing electrolyte to inside.

[0079] As described above, according to the present invention, accurate reaction control is enabled by destroying an active portion in the network structure of carbon in nano-size substance selectively using an electrochemical method. Consequently, the yield of the processing is improved, so that cost performance thereof is raised.

[0080] The present invention is not restricted to the above-described embodiments and description of the embodiments. The present invention includes various modifications not departing from the scope of claims and within a range which those skilled in art can imagine easily. 

We claim:
 1. A processing method for nano-size substance in which by applying an electric potential to nano-size substance having a carbon network structure at an outer shell thereof in electrolytic solution, an active portion in the nano-size substance is destroyed selectively.
 2. The processing method for nano-size substance as claimed in claim 1 wherein said nano-size substance is one types or two or more types selected from carbon nanotube, fullerene and carbon nano-horn.
 3. The processing method for nano-size substance as claimed in claim 1 wherein said nano-size substance has a space substantially closed by the outer shell having said network structure of the carbon, the space being released by destroying said active portion.
 4. The processing method for nano-size substance as claimed in claim 1 wherein the network structure of said carbon is composed of mainly six-membered ring structure while five-membered ring structure or seven-membered ring structure is possessed as said active portion.
 5. The processing method for nano-size substance as claimed in claim 1 wherein said potential is oxidizing potential of 1.00 to 1.60 V (RHE).
 6. The processing method for nano-size substance as claimed in claim 1 wherein said potential is oxidizing potential of 1.20 to 1.60 V (RHE).
 7. A production method for open-ended carbon nanotube in which by applying an electric potential to carbon nanotube in electrolytic solution, the active portion in the carbon nanotube is oxidized selectively so as to open the carbon nanotube.
 8. The production method for open-ended carbon nanotube as claimed in claim 7 wherein said active portion has the five-membered ring structure or the seven-membered ring structure.
 9. The production method for open-ended carbon nanotube as claimed in claim 7 wherein said potential is 1.00 to 1.60 V (RHE).
 10. The production method for open-ended carbon nanotube as claimed in claim 7 wherein said potential is 1.20 to 1.60 V (RHE).
 11. A production apparatus for open-ended carbon nanotube comprising: A working electrode capable of carrying nano-size substance having at least the network structure of carbon at an outer shell thereof; a counter electrode to the working electrode; a reference electrode which serves for reference upon setting an electric potential on said working electrode; and an electric potential source for applying an electric potential to each electrode, wherein said potential source supplies each of said electrodes with an electric potential so that active portion in nano-size substance having said network structure of carbon is oxidized or reduced selectively and the active portion is destroyed selectively. 